1. Field of the Invention
This invention relates to precipitation and dispersion hardening copper alloys and more particularly to precipitation hardening copper alloys that combine good mechanical and electrical properties.
2. Description of the Prior Art
There are many applications in which a strong resilient part having good electrical conductivity is desired. The superior conductivity of copper would make it an obvious choice were it not for its relatively poor mechanical properties such as comparative softness, low modulus of elasticity and low tensile and tensile yield strengths.
Unlike many kinds of steel, most copper alloys are not susceptible to improvement in hardness and strength by heat treatment processes. One useful exception to this is the copper beryllium alloys which are precipitation or age hardenable. These copper alloys, typically containing between 1 and 2% beryllium, are useful because of their non magnetic properties, good electrical conductivity, high tensile strength, high degree of hardness, and their ability to be cast, wrought, forged or drawn. Because of these properties they find utility in the manufacture of various types of instruments, electrical contact points, coil springs, non magnetic cutting tools and the like.
While copper beryllium alloys have useful mechanical and electrical properties, their cost is comparatively high due to the scarceness of beryllium in the earth's crust. Of even greater concern, is the current recognition that beryllium is an extremely toxic material and a hazardous carcinogen. This makes it difficult to process copper beryllium alloys with conventional techniques without exceeding exposure standards set by OSHA and endangering the health of workers. Copper beryllium alloys present a health hazard not only at the time the alloy is manufactured, but also during subsequent machining which produces air borne metallic dust particles.
Copper alloys using metals other than beryllium also have deficiencies. For example, brasses, phosphor bronzes, nickel silvers and most copper alloys obtain their property increases through cold working, which decreases formability in direct proportion to the amount of cold work. Other dispersion hardening alloys lack sufficient electrical conductivity to be used in electrical applications.
Accordingly, it is an object of this invention to provide a beryllium free precipitation hardenable copper alloy that has mechanical and electrical properties similar to those ordinarily only obtained with copper beryllium alloys.
Another object of this invention is to provide copper alloys that combine useful properties of tensile strength, yield strength, hardness, formability and electrical conductivity.
Another object of this invention is to provide a non toxic, relatively inexpensive, precipitation hardenable copper alloy that has desirable mechanical and electrical properties.
Briefly these and other objects of this invention are achieved by making a copper nickel alloy which includes minor quantities of silicon, chromium and aluminum. To achieve the desired mechanical properties at least 2% nickel (all percentages given herein are based upon weight) is required and the practical upper limit, from the standpoint of electrical conductivity is about 9%. The silicon, chromium and aluminum are all required, at least in small amounts, of from about 1/20% to up to about 2%. Within these limits, a large number of alloys can be made. No specific percentages can be given as ideal since, as is so often the case, an increase or decrease in a particular component is a trade off of one desirable property for another and the exact formulation selected will depend on the end use requirements. In one preferred formulation, however, the total of the silicon, chromium, and aluminum total about 2% or slightly less.
To the fullest extent possible, all but trace amounts of other metals should be excluded from the alloy as even small amounts of elements such as manganese and magnesium which are sometimes included in copper alloys, will significantly reduce conductivity and decrease ductility.
For most end use application, it is generally desired to achieve a conductivity of at least a 14% I.A.C.S. (Internation Association of Conductivity Standards.)
The alloys of this invention have a very complex structure of the various pseudo-binary systems with copper as the base component and the other elements combined in various combinations as the other phases. The alloy has increased solubility at elevated temperatures and this alpha state can be maintained by rapidly quenching to room temperature, thereby creating an unstable, super saturated condition that only requires the proper temperature to precipitate the hardening phases.
The alloys of this invention are readily hardenable at surprisingly short times at elevated temperatures. For example, maximum hardness is obtained in less than 2 hours, but, when the temperature is raised to about 750.degree. C., maximum hardness is developed in only 15 seconds.